22 Varietäten, Descendenz, Hybriden, 



A culture of Capsella Bursapastoris proved heterozygotic, yiel- 

 ding certain new forms (X C. Bursa-pastoris Setchelliana , X C". 

 Bursa-pastoris Treleaseana, X ^- Bursa-pastoris arachnoidea and X 

 C. Bursa-pastoris attenuata), as well as certain forms already descri- 

 bed by Shull (C. Bursapastoris rhomboidea and siniplex) in the 

 Proportion 4:2:4:2:3:1. The distinction between siniplex and 

 rhonihoidea, both inter se and between them and the other lorms, 

 is readily made by any one familiär with Shull's investigations. 

 These two plants agree in having the earlier leaves broad. The 

 climax leaves of rhomboidea and siniplex show marked differences, 

 especiallj^ as far as the incision of the blade is concerned. These 

 incisions. in sirnplex, reach a depth equal to approximately one 

 fourth ot the width of the blade. In rJiojnboiden the incisions are 

 deeper, reaching the midrib in the homozygous form. The leaves of 

 the latter also show marked secondary lobes. 



The distinction between X C- Bursa-pastoris SetcheUiana, X ^ 

 Bursa-pastoris Treleaseana and X C. Bursa-pastoris attemiata is 

 made with greater difificulty. They agree in having long and narrow 

 first leaves. The climax leaves o^ Treleaseana and SetcheUiana show 

 marked incisions, exceeding one fourth of the width of the blade, 

 and which may reach the midrib. The latter form also may show 

 marked secondary lobes. 



Besides the phenotypes here mentioned occur two others, the 

 one, X C. Bursa-pastoris orbiciilaris, with an almost orbicular tirst 

 leaf and a climax leaf greatly resembling that of simplex, though 

 differing in texture. This form has not been sufificiently studied , but 

 is believed to be identical with one known to occur in Europe. 

 Finally there is X C. Bursa-pastoris arachnoidea^ a sterile, linear- 

 leaved form, with a weak stem and which frequently shows fascia- 

 tion. To facilitate a distinction between these forms, a kcy is 

 appended: 



a. Early leaves broad 



b. Early leaves orbicular orbiciilaris. 



bb. Early leaves twice as long as broad 



c. Climax leaves incised to midrib .... rhomboidea. 

 cc. Climax leaves not incised to midrib . . simplex. 

 aa. Early leaves long and narrow 



b. Early leaves acicular arachnoidea. 



bb. Early leaves 21/0—3 times as long as broad. 



c. Climax leaves not incised to midrib . . attenuata. 

 cc. Climax leaves incised to or almost to the midrib. 



d. Secondarjr lobes pronounced . . . Treleaseana. 

 dd. Secondary lobes absent SetcheUiana. 



It was found that, besides the genes A, B, C and D, whose 

 existence was shown by Shull, there exists another gene, N, res- 

 ponsible for the narrow character of the earlier leaves. For the 

 various forms, mentioned here, the following zygotic constitutions 

 have been tentatively determined: simplex, bbnn; rhomboidea, )o,^nn 

 and Bbnn; SetcheUiana BbNn; Treleaseana BBNn; attenuata bbNn ; 

 arachnoidea BBNN, BbNN and bbNN. The zygotic Constitution of or- 

 bicularis has not been determined. 



As to the probable origin of X Bursa-pastoris SetcheUiana, little 

 can be said. It most probably results from a cross between rPiom- 

 boidea and attenuata fBBnn X bbNn). This seems the most plausible 

 explanation since, judging from hcrbarium specimens, both attenuata 

 and rhomboidea occur throuffhout the United States. Unfortuna- 



